Corrosion inhibitor mixture

ABSTRACT

Aqueous acid solutions are inhibited against corrosion of metals, especially ferrous metals, by incorporation of a corrosion-inhibiting mixture composed of a combination of 1hexyn-3-ol, 5-decyn-4,7-diol and urea.

United States Patent Tedeschi et al.

[151 3,655,571 [451 Apr. 11, 1972 [54] CORROSION INHIBITOR MIXTURE [72] Inventors: Robert J. Tedeschi, Whitehouse Station;

Paul W. Natali, Middletown, both of NJ.

[73] Assignee: Air Products and Chemicals, Inc., Allentown, Pa.

[22] Filed: Dec. 31, 1968 21 Appl. No.: 789,022

[56] References Cited UNITED STATES PATENTS 2,485,528 10/1949 Cardwelletal ..252/149 3,231,507 l/1966 Bealeetal. ..252/146 3,382,179 5/1968 Keeneyetal.... ..252/l48 3,428,566 2/1969 Herman etal. ..252/146 OTHER PUBLICATIONS Rutledge, T. F., Acetylemic Compounds, Rheinhold Book Corp., 1968 Primary Examiner-Leon D. Rosdol Assistant Examiner-Amold I. Rady Attorney-Barry Mayermon and B. Max Klevit [5 7] ABSTRACT Aqueous acid solutions are inhibited against corrosion of metals, especially ferrous metals, by incorporation of a corrosion-inhibiting mixture composed of a combination of lhexyn-3-0l, 5-decyn-4,7-diol and urea.

4 Claims, No Drawings 1 CORROSION INHIBITOR MIXTURE This invention relates to the inhibition of metal corrosion in' acidic solutions and is more particularly concerned with inhibited-aqueous acid solutions suitable .for the treatment of metals.

Metal cleaning baths and pickling baths generally comprise aqueous solutions of inorganic acids such as sulfuric acid,

' hydrochloric acid, and phosphoric acid, and are useful in the cleaning and treatment of iron, zinc, ferrous alloys, and the like. r

In the use of aqueous acidic baths to treat metals, additives or inhibitors in the baths are desirable to prevent or inhibit corrosion or erosion of the metal surfaces. Similarly, in the field of oil-well acidizing, it is necessary to use inhibitors in loss, production of undesirable metal surface properties, ex-

cessive consumption or loss of acid, and like adverse results will be experienced. Many different types of inhibitors have been proposed, but there has been a continuing search for corrosion inhibitors which can be used' effectively in small co'ncentrations, and which are economical to produce, since the use of inhibitors is a necessary expense and it is economically prudent to keep this expense at a minimum while, at the same time, realizing the desired inhibition of metallic corrosion or consumption. The need is also for corrosion-inhibitors which are effective at high temperatures, e.g. 200 F. and above, such as are encountered in various operations involving acidic solutions, particularly oil-well acidizing where higher and higher temperatures are' encountered asthe well extends further into the earth.

While various corrosion-inhibiting agents have been proposed, all of such agents are not of equal effectiveness and of the many hundreds of agents which have been contemplated, only a few are sufficiently active to be commercially attractive. This is particularly true in the'case of high-temperature operations. Some inhibitors which have been proposed are reasonably effective at low and moderate temperatures, but fail completely when high temperatures are encountered.

There has, therefore, been a continuing search for more effective inhibitors, or for ways of making a given inhibitor more effective. This search has involved the discovery of combinations of inhibitors which act together to provide an inhibitor mixture. However, many of these mixtures involve relatively expensive components so that, while they may be relatively effective in their corrosion-inhibiting activity, there are disadvantages from an economic standpoint, particularly if they have to be used in substantial quantities in order to bring about the desired corrosion-inhibiting activity. Similarly, many of these systems are ineffective at elevated temperatures. In particular, there is a need for a corrosion-inhibiting mixture comprising a plurality of components wherein relatively inexpensive compounds of poor corrosion-inhibiting ac-' tion can be catalyzed or potentiated by the other component or components of the mixture so that the combination has a high corrosioninhibiting activity even at elevated temperatures.

It is accordingly an object of this invention to provide a novel corrosion-inhibiting system involving a combination of agents which is highly effective from the standpoint of corrosion-inhibiting activity and which is, at the same time, commercially attractive.

It is a further object of this invention to provide a novel corrosion-inhibiting mixture comprising a combination of agents wherein one agent has a strong potentiating or catalyzing action upon the other agent so that the corrosion-inhibiting effectiveness of the combination is greater than the additive action of the components of the combination.

It is another object of the invention to provide a corrosioninhibiting mixture of the character indicated which is effective at high temperatures.

In accordance with this invention, it has been discovered that the above and other objects can be achieved by the provision of a corrosion-inhibiting mixture comprising a combination of 1-hexyn-3-ol, 5-decyn-4,7-diol, and urea. The ratios among these components of the corrosion-inhibiting mixture may vary, but the best results are obtained with weight ratios of the two acetylenic alcohols to each other ranging between 1:10 and :1, preferably between 1:5 and 5:1, and most suitably between 1:2 and 2:1, and with the weight ratios of the combined acetylenic alcohols to urea ranging between 1:5 and 10:1, preferably between 1:5 and 5:1, and weight ratios between 1:2 and 2:1 being especially preferred.

The acetylenic alcohol-urea inhibitor mixture of this invention is useful, in general, in the inhibition of corrosion of metal surfaces in contact with aqueous mineral acid solutions, such as hydrochloric acid,- sulfuric acid, and phosphoric acid, for

, example in the acidizing of oil wells, in electrolytic cleaning baths, and electrolytic refining of metals, as well as in metal cleaning and pickling baths. The use of the above-described inhibitor mixture of this invention for corrosion inhibition of metals in aqueous mineral acid solutions is advantageous in that this corrosion inhibitor mixture can be employed in such acid solutions over a wide and useful concentration range. A further advantage of this inhibitor mixture is that it may be used at elevated temperatures to provide satisfactory corrosion inhibition, even when in relatively low concentration.

. The most effective amount of the corrosion-inhibiting mixture to be used in accordance with this invention can vary, depending upon local operation conditions. Thus, the temperature and other characteristics of the acid corrosive mixture may have a bearing upon the amount of inhibitor to be used. The higher the temperature and/or the higher the acid concentration, the greater is the'amount of corrosion inhibitor required to give'optimum results. In general, however, it has been found that a concentration of the corrosion-inhibiting mixture of the invention between 0.01 and 2 percent,

preferably between 0.01 percent to 1.2 percent, by weight of the aqueous acidic solution is an effective corrosion-inhibiting concentration, although higher concentrations can be used when conditions make them desirable, with a concentration between 0.05 percent to 0.75 percent by weight being of most general use, at elevated temperatures, .e.g. in the neighborhood of 200 F. The acidic solution can be dilute or concentrated and can be of any of the concentrations used in treating metals, e.g. ferrous metals, or for operations involving contact of acidic solutions with such metals, e.g. oil-well acidizing, and the like, for example 5 to percent. lri most operations of the character indicated, acid concentrations of 10-15 percent by weight are employed, and non-oxidizing inorganic acids are used. However, it is not intended to limit the invention to any specific use of acidic solutions or with respect to any specific metal or acid.

While the inhibitor mixture of this invention can be prepared from individual quantities of l-hexyn-3-ol and 5- decyn-4,7-diol, a particularly advantageous source of these two .chemicals is the reaction mixture obtained by the ethynylation of butyraldehyde with acetylene, using the wellknown reaction wherein butyraldehyde and acetylene are reacted in the presence of a catalyst in an inert solvent medium, most commonly an ether, the reaction being carried out at various temperatures but which generally lie in the range of 0 to 50 C. This reaction, which was originally proposed by Favorskii, and has been improved upon by several other workers, is well-described in the literature, and reference is made, for example, to the book Acetylenic Compounds by Thomas F. Rutledge (Reinhold Book Corp., 1968), especially pages 146 to 149, and to the footnotes referred to therein. In a typical operation the aldehyde and the acetylene are reacted in an acetal or an ether as the reaction medium at substantially atmospheric pressure at a temperature of 20 to 30 (3., using solid KOI-I as catalyst in amounts which are substantially stoichiometric (usually slightly in excess) with respect to the aldehyde, the acetylene being in excess of the stoichiometric quantity. The thus-produced mixture of l-hexyn-3-ol and decyn-4,7-diol will vary in composition somewhat, depending upon the specific reaction conditions, but the ratio of 1-hexyn- 3-ol to 5-decyn-4,7-diol usually lies within the range of 5:1 to 1:4, and most commonly is about 1:1 to 2:1. The inert reaction medium is readily separated by distillation, but minor amounts of the solvent, e.g. up to percent by weight or more, may be present and such presence does not interfere with the activity of the acetylenic hydroxy compounds. The mixture may also contain minor amounts of by-products produced by condensation, aldolization, or other reactions and are also unobjectionable. Such by-products may range up to 10 percent by weight but are usually less than about 5 percent by weight.

It will be understood that a reaction mixture of the character indicated is particularly attractive from a commercial standpoint since purification of the product of the ethynylation reaction is not required, yet the important benefits of the combination of l-hexyn-3-ol with 5-decyn-4,7- diol in the mixture of this invention are realized in the critical area of corrosion inhibition, i.e. high acid concentrations and high temperatures.

The following experiments will serve to illustrate the effectiveness of the corrosion-inhibiting mixture of this invention under severe corrosion conditions encountered in practical application:

The method used to determine the inhibiting properties of the mixture of the invention employs test specimens or coupons. To prepare the coupons, they are wiped with acetone to remove any residual oils or grease, and pickled for 1 minute in 10 percent hydrochloric acid to eliminate any scale and surface film. After pickling, the coupons are dipped in sodium bicarbonate solution, rinsed well in tap water, rinsed in distilled water, and finally dried with acetone. The clean and dry specimens are then weighed to the nearest 0.1 mg. In carrying out the evaluation, hydrochloric acid of percent by weight concentration is used in order to duplicate oil-well acidizing conditions. The inhibitor mixture is added to 4 02. test bottles, 100 ml. of the acid then added to each bottle; and the mixture shaken vigorously. The bottles are suspended in a constant-temperature bath consisting of a bell jar filled with ethylene glycol and equipped with a stirrer. The temperature is regulated to maintain the samples at 200 2 F. The bottles are placed in the bath one-half hour before the test coupons are added to insure temperature equilibrium. The weighed coupons, in duplicate, are then supported on glass hooks in the test bottles and the bottles are covered with watch glasses during the testing period of 16 hours. At the end of the testing period, the bottles are removed from the bath, the coupons withdrawn, rinsed with water, sodium bicarbonate solution, distilled water, and dried in acetone, then weighed to measure weight loss. Corrosion-inhibiting properties are conveniently expressed as percent inhibition, using the following formula:

% Inhibition wt. loss of blztttklgsvsztlfizfi test coupon X 100 ori inal wt. test cou on-w los c u lnhlbmon: g p t s of test 0 pon original wt. test coupon EXAMPLE Using the test procedure described above, the inhibitor mixture of the invention was evaluated for its effectiveness in preventing corrosion of steel, using 1 in. X 2 in. coupons cut from a 1/16-in. sheet of a mild steel having the following typical analysis: 0.15 percent max. carbon, 0.30-0.60 percent man anese, 0.04 ercent phosphorous, 0.05 percent sulfur, the alance iron. ach test sample was prepared by adding Inhibition Inhibitor 16 hrs. Hexynol 5-decyn-4,7-diol urea 99 None 0 The foregoing evaluation was repeated except that the weight ratio of the carbinol-glycol mixture to the urea was 4:1. Again a percent inhibition of 99 was recorded.

These tests show the positive action of the combination of hexynol, 5-decyn-4,7-diol, and urea in accordance with this invention, in inhibiting metal corrosion of commercial steel in an acid solution of high concentration at an elevated temperature only slightly below the boiling point of water, over a prolonged period of time. The results shown in the foregoing test data are obtained when an ethynylation reaction mixture comprising 1-hexyn-3-ol and 5-decyn-4,7-diol of the type described above is employed in combination with the urea. When the urea is directly added to the acetylenic carbinolglycol mixture, it is advantageous first to dissolve it in a small amount of water, e.g. a 25 percent aqueous solution, and then add the solution to the acetylenic alcohols.

It will be apparent that various changes and modifications may be made in the operations described in the foregoing without departing from the scope of the invention as defined in the appended claims. it is intended, therefore, that all matter contained in the above description of the invention shall be interpreted as illustrative only and not as limitative.

We claim: 1. A metal corrosion-inhibitor mixture, for use with aqueous solutions of mineral acids, consisting essentially of:

a. l-hexyn-3-ol b. 5-decyn-4,7-diol and c. urea; the weight ratio of (a) to (b) ranging from 1:10 to 10:1 and the weight ratio of (a) (b):(c) ranging from 1:5 to 10:1,

said mixture, when added to such aqueous solutions, in amounts ranging from 0.01 to 2 percent by weight thereof, effectively inhibiting corrosion at temperatures as high as 200 F.

2. The mixture of claim 1 wherein, further, the weight ratio of(a) (b):(c) ranges from 1:5 to 5:1.

3. A corrosion-inhibited mineral acid comprising an aqueous solution of the mineral acid and from 0.01 to about 2 percent by weight of a mixture consisting essentially of:

a. 1-hexyn-3-ol b. 5-decyn-4,7-diol and c. urea; the weight ratio of (a) to (b) ranging from 1:10 to 10:1 and the weight ratio of (a) (b):(c) ranging from 1:5 to 10:1, said mixture effectively inhibiting corrosion of metal surfaces by said acid at temperatures as high as 200 F.

4. The corrosion-inhibited acid of claim 3 wherein the weight ratio of(a) (b):(c) ranges from 1:5 to 5:1. 

2. The mixture of claim 1 wherein, further, the weight ratio of (a) + (b):(c) ranges from 1:5 to 5:1.
 3. A corrosion-inhibited mineral acid comprising an aqueous solution of the mineral acid and from 0.01 to about 2 percent by weight of a mixture consisting essentially of: a. 1-hexyn-3-ol b. 5-decyn-4,7-diol and c. urea; the weight ratio of (a) to (b) ranging from 1:10 to 10: 1 and the weight ratio of (a) + (b):(c) ranging from 1:5 to 10: 1, said mixture effectively inhibiting corrosion of metal surfaces by said acid at temperatures as high as 200* F.
 4. The corrosion-inhibited acid of claim 3 wherein the weight ratio of (a) + (b):(c) ranges from 1:5 to 5:1. 